Conventionally, for example, a spiral membrane element comprising a porous core tube and, spirally wound therearound, a unit comprising a feed-side passage material guiding a feed-side fluid to a surface of a separation membrane, the separation membrane separating the feed-side fluid, and a permeation-side passage material guiding to the core tube a permeation-side fluid separated from the feed-side fluid by permeating through the separation membrane has been known as a fluid separation element used in reverse osmosis, ultrafiltration, microfiltration or the like.
Such a spiral membrane element is usually manufactured by alternately piling up a feed-side passage material held between two halves of a folded separation membrane and a permeation-side passage material, applying an adhesive to edges (three sides) of the separation membrane in order to form a sealing portion for preventing a feed-side fluid and a permeation-side fluid from being mixed, thereby preparing a separation membrane unit, spirally winding one or more units thus prepared around a core tube, and sealing edges of the separation membrane.
Regarding the sealing method, for example, JP-A-7-204471 discloses a method of adhering the edges of the separation membrane by sealing the edges thereof with a hot-melt type tape-form adhesive, prefixing the adhesive and irradiating the adhesive with electromagnetic wave. However, in this method, the adhesive does not sufficiently impregnate into the inside of the separation membrane, so that the permeation-side passage and the feed-side passage cannot completely be parted. As a result, raw water cannot sufficiently be prevented from flowing in the permeation side. Specifically, as shown in FIG. 5, a porous layer 101b remains on a portion in which impregnation of an adhesive 102 into a separation membrane 101 is insufficient, thereby part of the raw liquid to be flown along an outer surface of the separation membrane passes thought the porous layer 101b to flow in the inside of the separation membrane 101 in a horizontal direction, and then mixes in the permeation side.
There is a method of preventing raw water from being permeated by using a large amount of an adhesive. However, this method poses the problem that where an adhesive is used in an amount larger than is necessary, thickness of the adhesive is ununiform, resulting in the problem when winding a membrane leaf around a core tube such that wrinkles are easy to occur.